M MORALES¹, V SENTCHILO¹, J VAN DER MEER<sup>1

1</sup>Department of Fundamental Microbiology. University of Lausanne. Biophore. UNIL-Sorge. Lausanne. 2015.

The natural recovery of the soils polluted by aromatic hydrocarbons such as BTEX (benzene, toluene, ethylbenzene and xylene) can be enhanced by introducing specific biodegrader bacteria in a process named bioaugmentation. Owing to their unique metabolic properties and to their adaptation potential these bacteria survive and propagate in the contaminated environment at the expense of the degraded pollutant. In this project we study the adaptive response of the BTEX biodegrader Pseudomonas veronii 1YdBTEX2 in laboratory scale microcosms. We performed an RNA-seq metatransciptomic analysis of the immediate genome-wide transcriptional response of P. veronii 1YdBTEX2 to toluene in the non-sterile soil environment and compared it to that in liquid medium. One hour exposure to toluene triggered massive transcription (up to 208-fold induction) of multiple gene clusters, among which those for toluene degradation pathway(s) and toluene efflux pumps, thus clearly underlining their key role in the adaptation. In addition we identified a variety of highly up-regulated genes coding for conserved hypothetical proteins, which would be interesting to follow up on. When comparing the transcriptome of the cells in liquid medium with that in sandy soil we found major changes in expression of genes involved with membrane functioning (e.g., lipid composition, lipid metabolism, cell fatty acid synthesis), with osmotic stress response (e.g., polyamine or trehalose synthesis, uptake of potassium) and putrescine metabolism. Stable growth and survival of P. veronii 1YdBTEX2 in the microcosms for extended periods of time (7-10 days) suggest that the immediate response mechanisms disclosed in this study are efficient for long-term establishment in the polluted soil.